PROJECT SUMMARY: The long-term goal of this research program is to understand the role of abnormal cardiac calcium (Ca) handling in the genesis of cardiac arrhythmias. Calcium entry through L-type calcium channels triggers release of sarcoplasmic reticulum Ca, which then initiates contraction (excitation contraction coupling ? ECC). In the previous funding period we focused on the role of abnormal calcium release from the sarcoplasmic reticulum, with extension of key findings to multi-cellular and in vivo settings. In the current proposal we consider the role of a recently recognized alternate Ca entry pathway, store-operated Ca entry (SOCE), in the myocardium. SOCE occurs when depletion of SR Ca is sensed by STIM1, prompting Ca entry via sarcolemmal ORAI1/TRPC channels. Cardiac SOCE has been implicated in the hypertrophic response and linked to enhanced arrhythmogenesis. Thus, the main goals of this proposal are to determine 1) how ECC and SOCE coexist in the cardiac myocyte, and 2) how abnormal interaction(s) between these systems in disease contributes to arrhythmias. The goals will be addressed through the following specific aims: Aim 1: Define the cardiac SOCE signaling microdomain and its relationship to the classical ECC domain; Aim 2: Define alterations in the SOCE micro-compartment and their arrhythmic mechanisms in congenital and acquired cardiac arrhythmic disease; and Aim 3: Assess the antiarrhythmic efficacy of targeting SOCE in the diseased heart. A combination of genetic and pharmacologic approaches will be used, with key findings in murine studies extended to human tissues. Our research team has extensive expertise in studying functional, and structural aspects of cardiac arrhythmogenesis, spanning from nanodomain signaling mechanisms to in vivo studies, allowing an integrated approach to execute the specific aims.